Technical Field
The present invention relates to a construction machine equipped with an exhaust purification function.
Background Art
A selective catalystic reduction (SCR) apparatus is an example of apparatuses for purifying NOx in exhaust gas of a diesel engine.
With an SCR apparatus, there is a problem in that, when an engine is stopped by turning off an ignition key or the like, a temperature of a dosing valve rises due to residual exhaust gas in an exhaust tube and causes urea water to deteriorate in the dosing valve. In consideration thereof, Japanese Unexamined Patent Publication No. 2012-17687 discloses a technique involving, based on exhaust gas temperature when an engine is stopped, setting a cooling time required for a temperature of a dosing valve to drop to a temperature at which urea water is less likely to deteriorate, and injecting urea water from the dosing valve until the cooling time lapses from the moment the engine is stopped in order to cool the dosing valve.
Japanese Patent No. 5562503 discloses a technique which involves counting the number of times an engine has been stopped when the temperature of an injection apparatus adopted to inject a reducing agent was high; and when a count value exceeds a first prescribed value, issuing a warning such as “Let engine idle, then turn off key.”
However, in Japanese Unexamined Patent Publication No. 2012-17687, since urea water is injected after the engine is stopped, there is a problem in that water content in the urea water evaporates and urea is deposited, and the deposited urea crystallizes and adheres to an exhaust tube or the like to cause clogging of the exhaust tube.
Since Japanese Patent No. 5562503 adopts “150” as the first prescribed value and the injection apparatus is repeatedly exposed to a high-temperature environment, there is a problem in that the injection apparatus cannot be sufficiently protected. In addition, since the cooling time is not calculated in Japanese Unexamined Patent Publication No. 2012-17687, an operator has no idea how long an idle time must continue before turning off the engine. Japanese Patent No. 5562503 has another problem in that, since the engine is turned off without the injection apparatus having been sufficiently cooled, the injection apparatus cannot be sufficiently protected.